Means for preventing arc back



H. SIMON 1,899,594

MEANS FOR PREVENTING ARC BACK Feb. 28, 1933.

Filed Sept. 16, 1930 Inventor: He] lm ut Simon,

His Attnrney.

Patented Feb. 28, 1933 UNITED STATES PATENT OFFHCE HELLMUT SIMON, OF BERLIN-FRIEDENAU, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK MEANS FOR PREVENTING ARC BACK Application filed September 16, 1930, Serial No. 482,854, and in Germany October 10, 1929.

My invention relates to electric systems comprising space discharge devices connected between alternating and direct current circuits, particularly to protective means for such devices, and its object is the provision of improved means for preventing damage therein due to arc-back.

In the operation of electric systems comprising mercury are devices trouble is frequently encountered as a result of arc-hack, and various expedients have been suggested heretofore to prevent damage from this source, for example, special arrangements of anodes, the provision of grids interposed between cathode and anodes, or the use of re verse current relays and switches.

In accordance with the present invention the problem of preventing damage due to areback is solved by the provision of means so arranged that the light radiated from the arc-discharge between anode and cathode is utilized for controlling the current flow in the mercury arc device. For this purpose I provide a suitable light-sensitive device, preferably a photo-electric cell, which is exposed to the light radiated from the arc in the discharge path to be controlled, and which is connected to devices for controlling the current in the system comprising the mercury arc device.

As is well known, during the half period in which current flows between an anode and cathode of a mercury arc device the mercury vapor in the anode-cathode path radiates light rays strongly while in the other half period, assuming that the mercury arc device is operating normally and that arc-back does not occur, the arc is extinguished and the discharge path is dark. In order that the photo-electric cell may cause the current control devices to be actuated at the proper time the cell is connected to a device which responds differently to the two half waves of an alternating voltage having the same frequency as the voltage impressed on the mercury arc device, and which responds in such a manner that the current controlling devices are actuated only when the photoelectric cell exposed to light due to arc-back and therefore radiated from the arc discharge path during that half period in which the discharge path is dark in normal operation.

The photo-electric cell is so arranged that therefrom, the photo-electric cell may be enclosed within a light-proof casing surrounding the given anode arm. In one arrangement in accordance with the invention, the photoelectric cell may be energized from a direct current source, in which case the anode and cathode of the cell are connected respectively to the positive and negative poles of this direct current source. Thus connectcd, a photo-electric cell permits the passage of current therethrough when its cathode is exposed to light. A current, therefore, flows through the cell during the half period in which current normally flows between the given anode and the cathode in the mercury arc device which is to be controlled, but no current flows in the cell during the half period when current normally does not flow between the anode and the cathode, since during this latter half period the arc discharge path is dark. If, however, areback affecting the given anode associated with the photo-electric cell occurs in the mercury arc device, a current will flow between the anode and the cathode in this device not only during the half period of normal flow but also during the half period when no current flows in normal operation, thereby causing the arc discharge path which was normally dark during the latter half period to become luminous. In case of arc-back, therefore, the photo-electric cell will be exposed to light during this half period in which the arc discharge path is normally dark and current will flow in the cell during both half periods. An embodiment of the invention in which the photo-electric cell is connected to a direct current source will be more fully described hereinafter.

he photo-electric cell may be so arranged that no current flows in the cell in either half to the latter voltage that a positive potential is impressed upon the cathode of the cell during the half period of normal current flow between the given anode and the cathode of the mercury arc device, and a negative potential is impressed upon the cathode of the cell during the half period in which no current flows in normal operation. During the first half period above described no cur-rent flows in the cell even though light iromthe arc discharge path in the anode arm or the mercury arc device strikes the cell cathode,

because the cell-cathode is positive'with respect to the cell anode during this half period. During the second half period also no current flows in the cell, although a negative potential is then impressed on the cell catl ode, because the arc discharge path in the given anode arm of the mercury arc device is dark. Therefore in normal operation of the mercury arc device no current flows in the photo-electric cell during either halt period. If, however, arc-back occurs, the cell cathode receives light, due to the arc-back, during the half period of normal no-current fiow between the given anode and the cathode of the mercury arc device, and since as above noted, a negative potential is impressed on the cell cathode during this half period, current fiows in the cell. This photo-electric cell current, after suitable amplification it required, may be transmitted to grid control apparatus, or to relay or switch devices which, for example, may be adapted to disconnect the mercury arc device from a voltage source or to insert protective impedances in series with the device, in order to prevent damage due to arc-back.

When using an amplifier arrangement in connection with the photo-electric cell it is frequently advantageous to operate the cell itself, not with alternating voltage, as'above described, but with direct voltage, and instead of using direct voltagefor the cathodeanone circuits of the amplifier to use an alternating voltage, for at least one of the amplifier tubes, having the same frequency as thatoi the voltage impressed on the mercury arc device but so phased with relation to the latter voltage that the anode of the amplifier tube is positive with respect to the amplifier cathode only during the half period of nocurrent flow between the given anode and the cathode of the mercury arc device. It is to be noted that in this case a photo-electric cell without valve effect may also be used.

This result is I current circuit (not shown).

In the case of arc discharge devices having several anodes, each anode arm may be provided with a photo-electric cell and all the cells may be arranged to act upon a common translating device, for example, a transformer whose secondary Winding is connected to an amplifier. The output circuit of the amplifier may be connected to a relay or the like which will then operate on occurrence of arc-back to protect the system from damage. It is obvious that instruments for the indication of instantaneous electrical values and recording instruments may be provided in the output circuit of the amplifier.

- The invention further contemplates the provision of a group of photo-electric cells, instead ofone cell, for each anode arm, for example, two cells in a differential arrange ment. in order to maintain a constant illumination of one of the cells, as may be required, light radiated from the cathode of the arc discharge device may be utilized for the purpose.

it is an especially advantageous feature of the invention that, in accordance therewith, existing electrical systems comprising arc discharge devices may be equipped with the protective arrangements herein described for preventing damage due to arcback.

My invention will be better understood from the following description when considered in connection with the accompanying drawing in which Fig. 1 is a diagrammatic view illustrating one embodiment of my invention and Figs. 2 and 3 are diagrammatic views illustrating modifications of the embodiment shown in Fig. 1.

Referring to Fig. 1, a space discharge device of the mercury arc type is shown connected between alternating current leads '11 and the terminals 12 and 13 of a direct Mercury arc device 10 comprises a cathode 14 and anodes 15, 16 connected to the secondary winding 17 of a transformer 18, the primary of which is connected to the leads 11. A light-proof casing 19 is arranged around the arm of anode 16 and a photo-electrical cell 20 comprising an anode 21 and cathode 22 is so mounted in the casing that'when a luminous discharge appears in the anode arm light therefrom falls upon the light-sensitive cathooe 22 of the cell. The cell cathode 22 is connected to the negative pole of a direct voltage source 23, the positive pole of which is connected through a resistance 2% to the cell anode 21. One end of the resistance 24 is connected to the grid of an electron tube 25 and the other end to the variable contact of a potentiometer 26 whereby the tube 25 is provided with a suitable grit bias from a voltage source 27. The anode circuit of tube 25 includes av relay 28, the purpose of which will appear hereinafter.

In the embodiment of the invention shown in Fig. l the anode voltage for amplifier tube 25 is not supplied from a source of direct voltage, as in usual practice, but is taken from the same alternating current source which supplies the transformer 18 connected to the anodes 15, 16 of the mercury arc device 10. The anode voltage for tube 25 is thus taken from leads 11, for example, by means of a transformer 29, and in such a manner, as by usual phase-shifting means which may comprise a variable condenser 30 associated with a winding of the transformer, that the voltage in the secondary winding of the transformer 29 is so phased with relation to the voltage between anode 16 and cathode 14 of mercury arc device 10 as to prevent the flow of current in the anode circuit of tube 25 during the half period in which current flows between anode 16 and cathode 14 in normal operation of the mercury arc device. The arrangement of the circuits which supply the anode voltage to tube 25 is such that during this half period a negative potential from transformer 29 is impressed on the anode of this tube. During the other half period, i. e., the half period in which in normal operation no current flows between anode 16 and cathode 14 of device 10, a positive potential from transformer 29 is impressed on the anode of tube 25. The grid voltage of tube 25 is, however, so adjusted, by means of potentiometer 26 and source 27, that during this half period of no current flow and consequent darkness in the arm of anode 16 the resulting anode current of tube 25 is too small to cause the relay 28 to operate. It will be seen, therefore, that relay 28 will not be caused to operate at any time during normal operation of the mercury arc device. If, however, arc-back affecting anode 16 of device 10 occurs, the

path between anode 16 and cathode 14 becomes luminous during the half period in which this path is normally dark, light from the discharge due to the arc-back then strikes cell cathode 22, and current begins to flow through the circuit including the photo-electric cell and resistance 24. The voltage drop due to the current flowing through resistance 24 compensates for the negative grid voltage due to the action of potentiometer 26 and source 27. Since, as above explained, the potential of anode of tube 25 is positive during the half period in which the discharge path in the arm of anode 16 is normally dark and becomes luminous on occurrence of arcback affecting this anode, therefore, when the grid voltage rises due to the current from the cell, a current flows in the anode circuit of tube 25. The anode current, thus flowing in response to the positive anode potential and to the rising grid potential, is suflicient to operate the relay28 which, in the present embodiment of the invention, is shown as closing contacts 31 and thereby actuating a switch 32 to disconnect mercury arc device 10 from the alternating current leads 11.

In the modification of the invention illustrated in Fig. 2 the photo-electric cell 20 is not connected to a source of direct voltage as in the embodiment of Fig. 1 but to a source of alternating voltage of the same frequency as that supplied to the mercury arc device 10. The voltage impressed on the photoelectric cell may be supplied by a transformer 33 connected to leads 11, the secondary being connected to the cell cathode 22 and to the cell anode 21, preferably through a resistance 24. Phase-shifting means which may include a condenser 34- associated. with a winding of the transformer 33 are provided whereby the voltage impressed on the photo-electric cell is so phased that a positive potential is impressed on the cathode 22 of the cell during the half period of normal current flow in the arm of anode 16 of device 10, and that a negative potential is impressed on cell cathode 22 during the other half period. It will be noted that, in the first half period above stated, since current is flowing in the arm of anode 16 the discharge path therein is luminous and light therefrom strikes cell cathode 22, but at the same time no current flows in the cell because during this half period the cell cathode is positive; in the second half period, although the cell cathode is negative, no current flows in the cell because in this latter half period no current normally flows in the arm of anode 16, the arc discharge path in the arm is dark, and no light strikes the cell cathode. Photo-electric cell 20, therefore, remains inactive at all times during normal operation of mercury arc device 10. In case, however, arc-back occurs affecting anode 16 the arc discharge path in the arm of this anode becomes luminous during the latter half period above stated and light strikes the cell cathode 22. Since, during this half period, the voltage impressed on the cell cathode by the-voltage supply and phase-shifting means is negative, a current flows in the circuit comprising the photo-electric cell 20 and resistance 24. The terminals of the resistance may be connected respectively to the grid of an amplifier tube 25 and to the variable contact 26 of a potentiometer shunting a source 2'? of grid bias potential. A relay 28, included in the anode circuit of tube 25, adapted to be operated by current from a suitable anode current source 35. The grid bias of tube 25, however, is adjusted to such a value that normal operation of mercury arc device 10 the anode current of tube 25 does not rise to a value sufhcient to operate the relay. But on occurrence of arc-back affecting anode 16 and device 10 the grid bias of the tube 25 is so changed by the voltage drop in resistance 24,

due to the current flowing in the photo-electric cell circuit, as to permit-flow of current in the anode circuit of the tube, whereby re layQS may be operated, for example as in the form of the invention shown in Fig. 1, to close contacts 31 in a circuit which controls a switch 32 adapted to disconnect mercury arc device from leads 11..

Fig. 3 illustrates embodiment of the invention wherein a plurality of anode arms of a'merc-ury arc device 10 are each provided with a photo-electric cell mounted thereon in the manner above described in connection with Figs. 1 and 2. The cells may each be supplied with alternating voltage of suitable phase through transformers 33, as in the system illustrated in Fig. 2. Each photo-electric cell circuit may include, in addition to the secondary or" the voltage supply transformer 33, one of the primaries 36, 37 of a transformer 38 having a secondary winding 39. As in the case of the single photo-electric cell system described in connection with Fig. 2, both of the cells shown in Fig. 3 as associated respectively withthe arms of anodes l5 and 16 remain inactive during normal operation of mercury. arc device 10. If, however, arc-back occurs in either of the anode arms current Will flow in the correspondin photoelectric cell circuit comprising a cell 20 and a primary 36 or 3? of transformer 38. The current thereby induced in secondary 39 may be applied to amplifier means adapted to operate a relay for the protection of the system against damage due to arc-back in a manner similar to that above described in connection with Fig. 2.

It is believed obvious that a plurality of photo-electric cells, arranged as shown in Fig. 3 on a plurality of anode arms of a mercury arc device, may each be supplied with a direct voltage instead of an alternating voltage, each photo-electric cell circuitthen being connected to a separate amplifier tube, and all or" the anode circuits of the amplifier tubes bein supplied with alternating voltage in the same manner as described in connection with the single photo-electric cell and amplilier associated therewith shown in Fig. 1. It will be readily understood that a relay corresponding to relay 28 may be adapted to be operated, on occurrence of arc-back in the mercury arc device, by the current flowing in the anode of that one of the plurality of amplifier tubes which is associated with the photoelectric cell affected by the armbaclr.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The combination with an arc discharge device comprising an anode and a cathode, of an element arranged to be responsive only to light from arc-back between said anode and cathode.

2. The combination of an arc discharge device comprising an anode and acathode, current-controlling means associated with said device, a light-sensitive element associated with said anode,and .means comprising said element operable only-when light due to arc-back between said anode and cathode falls upon said element, to control. the operation of said current-controlling means.

3. The combination of alternating and direct current circuits, anarc discharge device comprising an anode and a cathode, means to connect said device to said circuits, current-controlling means associated with one of said connection means, an element arranged to be responsive to light from the arcbetween said anode and cathode, and means comprising said element operable only when light due to arc-back afiecting said anode falls upon said element, to control the operation of said currentcontrolling.means.

4:. The combination ofan arc discharge device comprising an anode and a cathode, means to impress an alternating voltage on said anode, current-controlling means associated with said device, an element arranged to be responsive to light from the arc between said anode and cathode, means comprising said element to control the operation of said current-controlling means, a voltage supply device associated with said element, and means to impress on said voltage supply device a voltage of the same frequency as that impressed on said anode, said voltage supply device being soarranged that operation of said current-controlling means is prevented except when light due to arc-back between said anode and cathode falls upon said element.

5. The combination of an arc discharge device comprising an anode and a cathode,

means to impress analternating voltage on said anode, current-controlling means associated with said device, means comprising a light-sensitive element associated with said anode to control the operation of said "current-controlling means, a voltage supply device associated with said element, means to impress on said voltage supply device a voltage of the same frequency as that impressed onsaid anode, and phase-shifting means associated with said voltage supply device to prevent operation of said current-controlling means except when light due to arc-back between said anode and cathode falls upon said element.

6. The combination of an arc discharge device comprising an' anode and a cathode, means to impress an alternating voltage upon said anode, current-controlling means associated with said device, alight-sensitive element having a cathode and arranged to be responsive to light from the arc between said anode and cathode of said device, and means to impress on the cathode of said element an alternating voltage of the same frequency as that of the voltage impressed on said are discharge device anode and so phased that the potential impressed on said cathode of said element is positive during those half periods of the alternating voltage impressed on said are discharge device anode in which current normally flows between said anode and cathode of said device and that said potential is negative during those half periods of said voltage impressed on said anode of said device in which no current normally flows between said anode and cathode of said device, to prevent operation of said. currentcontrolling means except when light due to arc-back between said anode and cathode of said device falls upon said cathode of said element.

7. The combination of an arc discharge device comprising an anode and a cathode, means to impress an alternating voltage upon said anode, current-controlling means associated with said device, a light-sensitive ele ment having a cathode and arranged to be responsive to light falling upon said cathode of said element from the are between said anode and cathode of said device, means to impress a direct voltage on said cathode of said element, an amplifier element connected to said light-sensitive element and comprising an anode and a cathode, and means to impress on said amplifier anode an alternat ing voltage of the same frequency as that of the voltage impressed on the anode of said device and so phased that the potential impressed on said amplifier anode is negative with respect to the potential of said amplifier cathode during those half periods of the alternating voltage impressed on said anode of said device in which current normally flows between said anode and cathode of said device and that said potential is positive during those half periods of said voltage impressed on said anode of said device in which no current normally flows between. said anode and cathode of said device, to prevent operation of said current-controlling means except when light due to arc-back between said anode and cathode of said device falls upon said cathode of said element.

8. The combination of an arc discharge device comprising an anode and a cathode, means to impress an alternating voltage on said anode, current-controlling means associated with said device, a light-sensitive element associated with said anode, an amplifier element comprising an anode, a control grid and a cathode, means comprising said amplifier element to operate said control means, means to impress a voltage on said grid in response to light falling upon said light-sensitive element from the arc between said anode and cathode of said device, and means connected to said amplifier element to impress a bias voltage on said grid to prevent operation of said current-controlling means except when voltage due to light from are back. between the cathode and anode of said are discharge device falling upon said light-sensitive element is impressed on said grid.

9. The combination of an arc discharge device comprising a cathode and a plurality of anodes, current-controlling means associated with said device, a plurality of lightsensitive elements each associated with a difterent one of said anodes, and means comprising said elements and operable when light due to arc-hack between any one of said anodes and said cathode falls upon that one of said elements which is associated with the anode affected by the arc-back, to control the operation of said current-controlling means.

10. The combination of an arc discharge device comprising a cathode and a plurality of anodes, current-controlling means ciated with said device, a plurality of lightsensitive elements each associated with a different one of said anodes, a transformer comprising a secondary winding and a plurality of primary windings each associated with a different one of said elements, and means comprising said elements and said transformer and operable when light due to arcback between any one of said anodes and said cathode falls upon that one of said elements which is associated with the anode affected by the arc-back, to control the operation of said current-controlling means.

11. The combination with an are discharge device comprising an anode and a cathode, of an element arranged to be responsive to light from arc back between said anode and cathode, and means to render said element unresponsive to normal illumination between said anode and cathode.

12. The combination of an arc discharge device comprising an anode and a cathode, current-controlling means associated with said device, a light-sensitive element associated with said anode, means comprising said element operable when light due to are back between said anode and cathode falls upon said element to control the operation of said current-controlling means, and means to render said cm'rent-controlling means inoperative when normal illumination from the are between said anode and cathode falls upon said element.

13. The combination of alternating and direct current circuits, an arc discharge device comprising an anode and a cathode, means to connect said device to said circuits, current controlling means associated with one of said connection means, an element arranged to be responsive to light from the are between said anode and cathode, means comprising said element operable when light due to arc back afiecting said anode falls upon said element to control the operation of said current-controlling means, and means to render said current-controlling means inoperative when normal illumination from the are between said anode and cathode falls upon said element.

145. The combination of an arc discharge device comprising an anode and a cathode, means to impress an alternating voltage upon said anode, current-controlling means associated with said device, a light-sensitive element having a cathode and arranged to be responsive to light from the'arc between said anode and cathode of said are discharge device, means to impress a direct voltage on the cathode of said light-sensitive element, an amplifier element comprising an anode and cathode and control grid, means to impress upon the anode of said amplifier element an alternating voltage of the same frequency as 7 that of the voltage impressed upon'the anode of said are discharge device and of opposite phase, meanscomprising said amplifier element to operate said current-controlling means, means to impress a postivc bias voltage upon said grid in response to light falling upon said light-sensitive element from the are between the anode and cathode of said are discharge device, and means connected to the amplifier element to impress upon the control grid a bias voltage opposing said positive bias voltage to prevent operation of the current-controlling means except when voltage due to light from are back bet-ween the cathode and anode of said arc discharge device falling uponsaid-light-sensitive device is impressed upon said grid. o

15. The combination of an arc discharge device comprising an anode and a cathode, means to-impress an alternating voltage upon said anode, current-controlling means associated with said device, a light-sensitiveele ment having a cathode and arranged tobe responsive to light fromthe are between said anode andcathode of said are dischargedevice, and amplifier element comprising an anode and cathode and control grid, means to impress a direct voltage upon the anode of the amplifier element, means comprising the amplifierelement to operate said currentcontrolling means, means to impress a positive bias voltage upon said grid in response .1 only to light falling upon the light-sensitive element from arcback between the anode andcathode of said are discharge device, said last-named means including means to impress upon the cathode of the light-sensitive element a voltage of the same frequency and phase as that of the voltage impressed upon the anode of the arc discharge device, and means connected to the amplifier element to impress a negative bias voltage upon said controlgridto prevent operationof said current-controlling means except when said postive bias voltage is impressed upon the grld. y

In witness whereof I have hereunto set my hand this 26th day of August, 1930.

HELLMUT SIMON. 

